High-throughput characterization of composition,microstructure and hardness distribution in X80 pipeline steel girth welded joints

Conventional characterization methods often fall short in accurately capturing the micro-regional heterogeneity of X80 pipeline steel girth welded joints. Multi-scale high-throughput characterization techniques, including micro-beam X-ray fluorescence spectroscopy, high-throughput scanning electron microscopy, electron backscatter diffraction, micro-Vickers hardness and nanoindentation, were employed to systematically investigate the composition, microstructure, hardness distribution and their correlations across different characteristic zones of the joint. Higher concentrations of Mn, Cu, Nb, Mo and Cr were observed in the heat-affected zone, while Ni, V and Ti were more abundant in the weld metal. Elements such as Mn and Nb promoted the formation of bainite, whereas Ni and Ti facilitated the formation of finely dispersed M-A constituents and acicular ferrite, respectively. The intercritical region exhibited the highest hardness, attributed to the presence of abundant granular bainite, elongated chain-like M-A constituents at grain boundaries (area fraction of 15.2%), and a high dislocation density. In contrast, the fine-grained region showed the lowest hardness, due to a higher content of the soft polygonal ferrite phase and a lower dislocation density.